Preserving Potmetal

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2012: Preserving Potmetal
Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Saturday, November 17, 2012 - 09:45 am:

My early Stewart 26A speedo has a potmetal body in a thin brass case. Is there a way to preserve the potmetal so it won't swell and destroy this rare item?



For the torture I give it, I really should pass this speedo on to somebody with a 1909, but I think the odo windows are so cool compared to the later 26 with drum odo.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jay - In Northern California on Saturday, November 17, 2012 - 10:44 am:

Ralph, Preserving potmetal? Now that's an oxymoron.:-) If your fortunate enough to have one of the very rare units that was blessed off the assembly line (kinda like Kosher salt is) your in luck otherwise it's just a matter of time before it embrittles,swells or crumbles.

Here's some info I snagged from the net.
Pot metal, also known as monkey metal, white metal or die-cast zinc, is a slang term that refers to alloys that consist of inexpensive, low-melting point metals used to make fast, inexpensive castings. There is no scientific metallurgical standard for pot metal; common metals in pot metal include zinc, lead, copper, tin, magnesium, aluminium, iron, and cadmium. The primary advantage of pot metal is that it is quick and easy to cast. Due to its low melting temperature no sophisticated foundry equipment is needed and specialized molds are not necessary. It is sometimes used to experiment with molds and ideas before using metals of higher quality. Examples of items created from pot metal include toys, furniture fittings, tool parts, electronics components, and automotive parts.citation needed Pot metal can be prone to instability over time, as it has a tendency to bend, distort, crack, shatter, and pit with age. The low boiling point of zinc and the fast cooling of the newly-cast part often allow air bubbles to remain within the cast part, weakening the metal. Many of the components of pot metal are susceptible to corrosion from airborne acids and other contaminants, and the internal corrosion of the metal often causes the decorative plating to flake off.citation needed Pot metal is not easily glued, soldered or welded. At one time, "pot metal" referred to a copper alloy that was primarily alloyed with lead. 67% Cu, 29% Pb & 4% Sb and 80% Cu, 20% Pb were common formulations.1 The primary component of pot metal is zinc, but often the caster adds other metals to the mix to strengthen the cast part, improve the flow of the molten metal, or to reduce cost.dubious – discuss With a low melting point of 419 °C (786 °F), zinc is often alloyed with other metals including lead, tin, aluminium and copper. See also Babbitt (metal) Zamak Zinc aluminium Zinc pest References ^ Balfour, Edward (1885), The Cyclopædia of India and of Eastern and Southern Asia, 3 (3 ed.), London: Bernard Quaritch, p. 271 This alloy–related article is a stub. You can help Wikipedia by expanding it.v · d · e


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jem Bowkett on Saturday, November 17, 2012 - 11:06 am:

Well Ralph, if you're looking for a 1909 home for that speedo....


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Saturday, November 17, 2012 - 11:36 am:

Could a replacement body be made in brass?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Saturday, November 17, 2012 - 11:46 am:

Good to hear from you, Jem. Haven't seen you post in a long time.

Here's a 26B the seller says is right for 1911, for only $800. It looks the same as the 26A, anyhow.

http://www.ebay.com/itm/STEWART-SPEEDOMETER-NO-26-MODEL-T-FORD-BRASS-ERA-1911-AN D-EARLIER-RESTORED-/281019392127?pt=Vintage_Car_Truck_Parts_Accessories&hash=ite m416e0fa07f&vxp=mtr

Mine doesn't look quite so nice.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Saturday, November 17, 2012 - 11:49 am:

You might be onto something, Steve. I'll take some pix to show the situation.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Saturday, November 17, 2012 - 11:50 am:

If you have any room at all in there Ralph, J-B Weld is about the best way of holding things together. I've done this on pot metal tuning condensers on many 1920's radios. Put a thin coating over everything you can get at. The only problem with J-B Weld is that it will run due to gravity as it is very slow setting ... there is a second version called J-B Quick which would be better.

Garnet


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Saturday, November 17, 2012 - 02:35 pm:

Pot Metal tends to break down at the atomic level. Some believe it is caused by impurities in the molten material (for instance, the high failure rate of pre-war American Flyer toy train cast bodies is attributed to workers throwing their foil gum wrappers into the pot). If it hasn't "swollen" yet, you probably have a good "mix" for your casting. Humidity is also a contributing factor as well as heat. Don't know if it would do anything, but am wondering if an application of "Crazy Glue" would help seal the metal from atmospheric exposure?
T'
David D.


Top of pagePrevious messageNext messageBottom of page Link to this message  By william schaller on Saturday, November 17, 2012 - 02:59 pm:

Thermal cycles will cause failure.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jay - In Northern California on Saturday, November 17, 2012 - 03:06 pm:

David, I agree it happens at the atomic level but once the die is cast(excuse the pun) nothing you do can change the end result when your pot metal starts showing signs of trouble. even it you put it in an inert environment, once it's begun it's out of the hands of mere mortal men IMHO.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Saturday, November 17, 2012 - 03:14 pm:

David is correct about the atomic level break-down. The metals begin to interact like a battery to produce oxides. Die cast alloys will corrode from the inside out. That's why it swells. Sealing the surface is a short term fix as the corrosion will continue and crack the surface coating. Once the surface coating is cracked, moisture gets to the subsurface and corrosion accelerates there. That's why you see "bubbles" in old plated die cast parts.

There's no real fix except to replace the part. I won't even try to re-plate old die cast parts any more unless it's a one of kind piece. The cost to repair the corrosion damage on the surface just isn't worth it. And there's no guarantee that the corrosion "pops" won't return in the future since it's still corroding internally.

The only good thing about die cast is that it allows more detail to be provided in the casting process--Much more than brass. The drawback is that it doesn't last.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Saturday, November 17, 2012 - 06:38 pm:

Ricks

David Dewey had an interesting idea with the crazy Glue (Cyanoacrylate).

Since there appears to be no known way to arrest the changes in the metal, light coatings of Cyanoacrylate might do the trick. Most of these types of glue have a very low viscosity and will easily penetrate porous materials and hairline cracks. Actually it does not do well glueing porous materials (like a balsa wood joint) because it wicks away so fast it leaves no adhesive at the joint. That's why they make a gel.

You might wind up with a sort of composite material tightly bound together with adhesive. Hopefully still functional. It would certainly retard the penetration of the metal by oxygen which might retard further corrosion

Yes it sounds Rube Goldberg, but if there is no other alternative what have you got to lose? You would have to be careful that the Cyanoacrylate doesn't get on any bearing surface.

If I were to try it I would get a GOOD grade of Cyanoacrylate, perhaps from Locktite. Stay away from the chinese 25 cent disposable packets.

Maybe we have an adhesive expert on the Forum who will comment?

schuh


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jay - In Northern California on Saturday, November 17, 2012 - 07:03 pm:

I believe once the deterioration has begun the already oxidized metal supplies the oxygen to cancer out more material even when sealed from the atmosphere. I would also think the galvanic action between the various metals in the speedometer would help to advance the deterioration.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Saturday, November 17, 2012 - 07:20 pm:

Russ F would know much more about this than I ever will. New bodies could be cast without too much difficulty. It would probably take a lot of expensive time to set up the molds, and machining would have to be VERY precise. The problem then would be that there are so many models and variations of speedometers that what you make will only work for a very few.
If you have a functioning unit that has not distorted much, you could try a "lost wax" method of casting. Artist foundries usually do this. With a little luck, you may be able to compensate for the thermal shrinkage when you machine the casting. If you cannot, you would have to go to greater effort in mold making and modify the dimensions to allow for thermal shrinkage.
I am not an expert in any way shape or form on this subject, I have read up on it a few times while considering trying it to save or replace old pieces. I would consider using aluminum as it is also fairly easy to work with, and looks similar to pot metal.
Drive carefully, and enjoy, W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Saturday, November 17, 2012 - 07:41 pm:

Wayne - Die casing is much more involved than a cope and drag. You can't just poke a hole in the sand and make a die cast part. As the name implies, you need mold dies. And these can get very complicated.

Perhaps someone can make one with a 3D scanner and printer. They can print metal now days and fire it like ceramic.


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Saturday, November 17, 2012 - 07:49 pm:

I think one reason they used the zinc is that it tends to shrink less. I know when you look at the castings for window regulator gear cases they show no sign of machine work except for the threaded holes. I keep thinking I'll get around to trying some of those one day. Another thing on the to do list. Think I'm running out of time. KB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Saturday, November 17, 2012 - 08:12 pm:

I think they use zinc because it's cheap. By itself, it's one of the metals that shrink the most. It has a HUGE shrinkage factor. I use pure zinc for making press dies and have to allow .030-.040" shrinkage on parts that are no more than about 1-2 square inches.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Saturday, November 17, 2012 - 08:45 pm:

I just field stripped it, guys, as it has had the habit of jumping at around 40-50 mph, the speed I drive on our boulevards, and I want to preserve it.



Looks like potmetal to me, and too dense to be aluminum. There's not a bit of deterioration.

I'm going to start another thread on this, to not confuse the repair detail with all the potmetal ideas you've posted.

Thanks


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Saturday, November 17, 2012 - 09:19 pm:

Ken, if you were going to try and make these castings, what metal would you use? KB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Sunday, November 18, 2012 - 01:00 am:

Ken K, Oh, I know how complicated metal casting can be. But a little creativity can go a long way. I've seen some radiator caps done lost wax that make that speedometer body look like a square block.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Sunday, November 18, 2012 - 03:32 pm:

Wayne - Well of course. Lost wax is a totally different process and expensive. It's not sand casting as you mentioned in your previous comparison.

Keith - Make them for whom? Myself or for production? There's a big difference. For a one-off I'd go with aluminum. Probably cast then machine or just billet machine. Depends on the time I had. If I had to make 10,000 of them, you bet I'd go with a die cast process and alloy.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach & Big Bear on Sunday, November 18, 2012 - 04:14 pm:

A friend of mine, now long gone, used to clean pot metal hood ornaments and then bronze plate them sort of like they bronze baby shoes. It doesn't get hot enough to melt the leather with their system. Then he would chrome plate it.

When I was restoring our 66 XKE roadster I took the tail lights to a plater. They sanded off the pits and copper plated them then filled in the copper with solder, then copper plated the solder and then nickel and then chrome. They charged $60 each back in 1980.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Sunday, November 18, 2012 - 05:00 pm:

1980 dollars = $60
2012 dollars = $214-$240 EACH :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Russell Medhurst - Melbourne, Australia on Sunday, November 18, 2012 - 07:56 pm:

Like the message from Bud re glues, FWIW in Oz a loctite product has been used successfully to smear and successfully stabilise and seal the inside of pot/mud metal vintage motorcycle carbies successfully.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Sunday, November 18, 2012 - 11:10 pm:

Ralph,

I don't have to explain it, Ken has done a great job of that. Pot metal was junk metal to begin with and chances are no two surviving pieces are alike in composition.

Yours has held together tight for 100 years or so, may never scale or soften ever...but a good dose of moisture could just start it on its merry way even now. I don't have a recommendation at to 'what', but if it was me I'd look for a product that is watery thin, dries by evaporation and not cross-linking, doesn't breathe when dry, can be soaked off later with something simple that won't attack anything underneath. Do it after a few dry days with low humidity, and yeah, you may lock in some moisture, but so far 'some' as in normal atmosphere has done nothing. Don't even think of baking it as something might just decide to turn around and outgas causing new problems when done. If it was next to a toss-away, I'd maybe try...but what you have looks too good to 'try' a bake on.

BTW...based on a few other posts...is the ol' brass pickup' getting a little more than 'just' a tranny overhaul? Perceptive minds get curious :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Sunday, November 18, 2012 - 11:46 pm:

It would seem to me that if you were to reproduce it, the best way would be to hog it out of aluminum on a CNC machine. One of our club members, a retired computer professional has taken machining classes on CNC machines at one of our county junior colleges and has become quite proficient. Maybe you have a west coast compatriot who has done the same and can help you out. If you cast it, you will still have to machine it unless you make it an investment casting. I think once you get it going on an CNC machine you could make 10 almost as easy as you could make one. If you have an error a minor programming change would likely fix it.


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration